infants through about 3 monthsis either breast milk or formula. Formulas are imported and diluted coconut milk to supplement or replace the milk from breast- or bottle-feeding. For a concentrations. milk and 5% is a mixture of equal parts coconut contain very low concentrations of 99Sr representative of worldwide background daily total intake of 1.3 L/d, we assumethat, on the average, 95% of the daily intake is breast The concentration of Sr in breast milk ma milk and water. Consequently, the daily intake of %Sr from 4 to 8 months would be be determined from the OR. The ORTmule has been reported to be 0.10 (Loughet al., 1960; Comar, 1967), indicating a discrimination across 0.043 pCi/L(0.95) 13L/d + 0.016 pci/mi 2) 1300 mL/d = 0.053 pCi/d + 0.52 pCi/d the mammary barrier similar to that across the placental barrier. The OR is based uponthe Sr per g of calcium and consequently is not directly of use in dose calculations. Thetotal g of calcium in the reference and target must be known so that = 0.57 pCi/d, the total amount of 99Sr transferred from a where the concentration of Sr in coconut milk at Rongelap Island is 0.016 pCi/mL and in breast specific source to a specific target can be determined. A more convenient form for the data for dose calculationsto infants using current models is the 90Sr concentration per kg of mothers’ milk based on the mothers’ dietary intake. The average percentage of 99Sr ingested that is secreted per kg of milk was determined to be 0.31% for 4 women (Lough et al., 1960). milk is 0.043 pCi/L. Infant/Child (9 months to 1.4 y). At about age 9 months to 1.5 y, small quantities. of local foods are given to the infants to supplement breast-feeding. The estimated 9°Sr intake from consumptionof local foods is assumed to be 20% of the adult intake and is 2.8 pCi/d. Thus, the Using this average value for the percentage of 90Sr daily intake of 9°Sr is assumed to go from the 4- to 8-month-old value of 0.57 pCi/d to about average 99Sr daily intake of 14 pCi/d at 3.4 pCi/d. ingested that is secreted in milk and the Child (1.5 y to 3 y). Rongelap Atoll for women, the concentration of 90Sr per kg (~1 L) of milk would be 0.043 pCi/kg. Thus, assuming that an infant's diet is about 1.3 L/d of milk, the daily intake of 99Sr from Child (4 y to 11 y). birth through 3 months would be 0.056 pCi/d. The ORZt in the first few months after available is 8.2 pCi/d (Appendix A, Table A-3). Loutit, 1964; Lough et al., 1963; Comar, 1967); Teenage (12 y to 17 y). The average daily that is, the infant nearly equilibrates with his diet. The oR" changes to about 0.5 by 1 y and Loutit, 1964; Comar, intake of Sr for teenagers from our diet model when imported foods are available is 11 pCi/d (Appendix A, Table A-4). 1967; Kawamuraet al., 1986) and levels out at about the adult value of 0.25 by age 3 to 5 y (Lough Adult (2 18 y). The average daily intake of 90Sr for adults from our diet model when et al., 1960, 1963; Comar et al., 1965; Comar, 1967; Burton and Mercer, 1962). imported foods are available is 14 pCi/d This type of information has been incorporated in the retention model discussed later in the paper. Infant (4 to 8 months). We assumethat infants from 4 to 8 months occasionally receive I0001b4 The average daily intake of 29Sr for children 4-y to 11-y old from our diet model when imported foods are birth is about 0.9 (Comar et al., 1965; Bryant and (Bryant The average daily intake of 99Sr for the 1-y to 3-y age group from our diet model is 9.2 pCi/d (Appendix A, Table A-2). (Appendix A, Table A-1). The daily intakes of 9Sr for the various age groups, based on the data and assumptions described above, are summarized in Table 4. 10